As a technique for the electronic watermarking of audio data, there is a Spread Spectrum method, a method for employing a polyphase filter, or a method for transforming data in a frequency domain and for embedding the resultant data. The method for embedding and detecting information in the frequency domain has merit in that an auditory psychological model can be easily employed, in that high tone quality can be easily provided and in that the resistance to transformation and noise is high. However, the target for the conventional audio electronic watermarking technique is limited to digital audio data that is not compressed. For the Internet distribution of audio data, generally the audio data are compressed, because of the limitation imposed by the communication capacity, and the compressed data are transmitted to users. Thus, when the conventional electronic watermarking technique is employed, it is necessary for the compressed audio data be decompressed, for the obtained data to be embedded and for the resultant data to be compressed again. The calculation time required for this series of operations is extended for the advanced audio compression technique that implements both high tone quality and high compression efficiency. How long it takes before a user can listen to audio data greatly effects the purchase intent of a user. Therefore, there is a demand for a process whereby the embedding, changing or updating of additional information can be performed while the audio data are compressed. However, there is presently no known method available for embedding additional information directly into compressed digital audio data, and for changing or detecting the additional information.